1. Field of the Invention
This invention relates to an insole manufacturing process, more particularly to a process for manufacturing an ethylene vinyl acetate insole.
2. Description of the Related Art
In a conventional EVA (ethylene vinyl acetate) insole manufacturing process, an EVA resin is mixed with a foaming agent, and the mixture is then squeezed into strips. The EVA material strips are then placed in a hot press and subjected to a foaming process. After foaming, the foamed EVA strips are placed in a water-cooling trough for cooling. After cooling, the foamed EVA strips are cut and trimmed. In some instances, some pieces of trimmed EVA pieces are adhered together. After passing through a grinding process, the EVA strips thus obtained are placed in a hydraulic machine for form setting. Thus, a whole EVA insole manufacturing process is completed. This EVA insole manufacturing process is not satisfactory, because of the following disadvantages:
1. It requires much human power and processing time.
2. Much waste material is produced. Because EVA strips are cut and sheared after the foaming process, approximately 40% or more of the foamed EVA strips are cut off and become useless. Disposal of the waste material is still a problem to settle, and it may cause environmental pollution.
3. Dusts and powders are produced during the grinding process. The dusts and powders are harmful to the workers.
In another conventional insole manufacturing process, an EVA resin is mixed with a foaming agent, and the mixture is then melted and is cooled to form pellets in an extrusion machine. The pellets are melted in an injection-molding machine, and the molten EVA material is injected into a mold unit to form a foamed insole. The foamed insole is trimmed to obtain a final product. Although an EVA insole can be obtained rapidly via the injection molding process, the cost of the injection-molding machine is relatively high. In addition, since the precision requirement of the mold unit is relatively high, the cost of the injection-molding unit is two to three times the cost of an ordinary mold unit. Therefore, the injection-molding machine is not suitable for producing a small amount of EVA insoles of various styles or designs. Further, because the molten EVA material is injected into the mold cavity via the injection nozzle and the runners in the mold unit, wastes are present in the runners after the injection-molding machine is shut down. These wastes must be removed from the injection nozzle and the runners before a succeeding injection-molding operation is carried out. This inconveniences the operator.